Return to Winged Keels

[pschwenn]

In an earlier topic, three aspects of Wings (Winglets on Keels and Wings) were missed or understated, which might simplify understanding some of the questions raised.  Span constraints, inherent disadvantage, and design subtlety and difficulty.

Span Contraints.  Winglets on airliners might seem to be powerful evidence of their performance enhancement.  No; initially airports did not have enough large enough docking spaces for a wave of new aircraft on the way.  In boating, along with the multiplicity of old-age constraints on draft, the 12-metre AC rule had a 9' draft limitation.  The winglets on the AC boats fit the boats to the rule, deeper keels would have been superior (for performance) in all respects.  The winglets on airliners, initially, fit them into their parking spaces.

The 787, freed by larger spaces, exploits the advantage of not having winglets.  Its outer span has subtle shaping and shape changing flexibility which add to that advantage in a way that tacking on even clever winglets to unconstrained span do not - the A380 has little winglets both for marketing and to simplify adding virtual span long after the initial design.  Winglets are being marketed as well to all sorts of smaller General Aviation aircraft - both for span constraints in existing hangars, and for marketing, and, again, and ultralight tack-on is simpler in every way than redesign and renovation of an existing wing.

Difficulty & Subtlety of Increasing Effective Span.  Draft constraints on keels can be sharp, or just desirable, so the search for lower CG and greater effective span is quite legitimate.  But very difficult to get right.  Scheel headed in the right direction, but understandably, missed.  If someone other than Burt Rutan designs a Canard airplane, watch out.  If a team tacks winglets on a 12 metre without the insight and analysis of the early Australian boat, hold that bet.  The twin keels are a great alternative either side of the English Channel for sitting down gracefully when the tides out without resorting to stilts, but they are not a match for performance for the same effective deeper single span (and sitting down can be a lot worse than graceful.)

If Scheel had gone further: a gentler, truly progressive increase in foil thickness toward the base of the keel, and a near-sharp edge at the base as virtual fence (with zero surface area) for flow (pressure) escaping below, before reaching the trailing edge.  Perhaps progressing to a foil at the base which is net more effective at higher foil thickness.  It might have worked quite well.  Searching for lower VCG, "Marry it or Divorce it": a keel should lift, a bulb should be as invisible as possible (not easy), not lifting or dragging more than inevitable.

Inherent Disadvantage.  Winglets will only get you a virtual span increase of 1/2 or a little more of their own span.  And they'll generally have twice the surface area (or more), of simple span increase.  They'll introduce interference drags the simple span lacks. 

Advances in other keel shaping to reduce induced drag (the "bad" wake vortices) might change those deficits.  You won't have to wait for an example: Centerboards.

At first sight, a long post wouldn't seem to simplify anything, but sometimes seeing that a situation is simpler than it appears gets complicated.  

regards,

 

[SemiSalt]

A few years ago, my boat spent a winter on the hard surrounded by about 15 other wing keel boats. It was interesting to see how a more or less standard approach was stretched this way and that until no two were alike, even near sisters from the same designer-builder. Also interesting was how crude the shaping and construction was on a few.

 

[Zonker]

without some pretty sophisticated tank/wind tunnel/CFD most winged keels are pretty draggy and useless. At best they keep the VCG low with shallow draft.

 

[MikeJohns]

In an earlier topic, three aspects of Wings (Winglets on Keels and Wings) were missed or understated, which might simplify understanding some of the questions raised.  Span constraints, inherent disadvantage, and design subtlety and difficulty.

Span Contraints.  Winglets on airliners might seem to be powerful evidence of their performance enhancement.  No; initially airports did not have enough large enough docking spaces for a wave of new aircraft on the way.  In boating, along with the multiplicity of old-age constraints on draft, the 12-metre AC rule had a 9' draft limitation.  The winglets on the AC boats fit the boats to the rule, deeper keels would have been superior (for performance) in all respects.  The winglets on airliners, initially, fit them into their parking spaces.

The 787, freed by larger spaces, exploits the advantage of not having winglets.  Its outer span has subtle shaping and shape changing flexibility which add to that advantage in a way that tacking on even clever winglets to unconstrained span do not - the A380 has little winglets both for marketing and to simplify adding virtual span long after the initial design.  Winglets are being marketed as well to all sorts of smaller General Aviation aircraft - both for span constraints in existing hangars, and for marketing, and, again, and ultralight tack-on is simpler in every way than redesign and renovation of an existing wing.

Difficulty & Subtlety of Increasing Effective Span.  Draft constraints on keels can be sharp, or just desirable, so the search for lower CG and greater effective span is quite legitimate.  But very difficult to get right.  Scheel headed in the right direction, but understandably, missed.  If someone other than Burt Rutan designs a Canard airplane, watch out.  If a team tacks winglets on a 12 metre without the insight and analysis of the early Australian boat, hold that bet.  The twin keels are a great alternative either side of the English Channel for sitting down gracefully when the tides out without resorting to stilts, but they are not a match for performance for the same effective deeper single span (and sitting down can be a lot worse than graceful.)

If Scheel had gone further: a gentler, truly progressive increase in foil thickness toward the base of the keel, and a near-sharp edge at the base as virtual fence (with zero surface area) for flow (pressure) escaping below, before reaching the trailing edge.  Perhaps progressing to a foil at the base which is net more effective at higher foil thickness.  It might have worked quite well.  Searching for lower VCG, "Marry it or Divorce it": a keel should lift, a bulb should be as invisible as possible (not easy), not lifting or dragging more than inevitable.

Inherent Disadvantage.  Winglets will only get you a virtual span increase of 1/2 or a little more of their own span.  And they'll generally have twice the surface area (or more), of simple span increase.  They'll introduce interference drags the simple span lacks. 

Advances in other keel shaping to reduce induced drag (the "bad" wake vortices) might change those deficits.  You won't have to wait for an example: Centerboards.

At first sight, a long post wouldn't seem to simplify anything, but sometimes seeing that a situation is simpler than it appears gets complicated.  

regards,

Aircraft ……Aero and Hydro are considerably different fields and don’t make for good observations crossing between fields.

 Winged keels are really draggy outside of a narrow range of conditions. On boats they are more about getting ballast low than any real robust advantage. The real lift advantage from a winged keel is limited to smooth water  and a narrow range of headings and heel angle.

Scheel keel wasn’t a great design idea it was just well marketed but the shape didn’t come out of any rigorous testing regime, low aspect keels get their lift from vortice generation not from aerofoil effects. Rounding the bottom edge actually has an adverse effect on lift as it delays the cross flow vortice separation which isn’t what you want at all.   




Bulbs are really draggy too, but less so than trying to incorporate a NACA 0030 foil to get enough internal volume to get the ballast low and or keep the WSA low and or keep attached laminar flow on the foil..




Nothing ideal once you get away from an elliptically loaded aerfoil it’s all compromises and cycling through fads and fashions.

 

[SemiSalt]

 Winged keels are really draggy outside of a narrow range of conditions. On boats they are more about getting ballast low than any real robust advantage. The real lift advantage from a winged keel is limited to smooth water  and a narrow range of headings and heel angle.

What's the difference in the real world. Here are some comparisons of base ratings for some Catalina models (YRA/LIS data):

Catalina 270 - 198

Catalina 270W - 204

Catalina 34 - 156

Catalina 34 Wing - 165

Catalina 400 DK - 108

Catalina 400 W - 111

So the wing is assumed to have a penalty of 6-10 sec/mile around the whole race course. The upwind penalty is higher, but the offwind penalty is negligible, and the wing might actually be an advantage there. Cruisers sail upwind a smaller percentage of the time than racers. It's no wonder that cruisers find the wing keel boats satisfactory.  

 

[slap]

 The upwind penalty is higher, but the offwind penalty is negligible, and the wing might actually be an advantage there. Cruisers sail upwind a smaller percentage of the time than racers. It's no wonder that cruisers find the wing keel boats satisfactory.  

It's fairly common for shoal draft versions of boats to have more ballast than their deep keeled sisters to make up the loss in righting moment.    As an example, my boat has about 10% more ballast than the deep keel version.   And the shoal draft keel often has more wetted surface and drag than the deep keel.   So the shoal draft version can be slower on all points of sail.

My impression is that the wing keel fad has died down somewhat and most current production shallow draft keels just use a bulb like or flaired shape to get the ballast low enough for the required righting moment. 

Of course a shoal draft boat is far faster than a deep keel boat if the water is shallow enough.

 

[Grrr...]

And, to add on against a lot of what the OP said - the 'winglets' at the end of the wings on planes are there to increase overall efficiency and lift by reducing tip vortices caused by lack of an end plate.  Part of the same reason that the foiling AC boats started sealing the bottom of the mainsail up against their hull.

 

[SemiSalt]

So, get a block of basswood, unfold your pocketknife, and get to whittling..

View attachment Hunter_28_41178058.pdf

 

[slug zitski]

In an earlier topic, three aspects of Wings (Winglets on Keels and Wings) were missed or understated, which might simplify understanding some of the questions raised.  Span constraints, inherent disadvantage, and design subtlety and difficulty.

Span Contraints.  Winglets on airliners might seem to be powerful evidence of their performance enhancement.  No; initially airports did not have enough large enough docking spaces for a wave of new aircraft on the way.  In boating, along with the multiplicity of old-age constraints on draft, the 12-metre AC rule had a 9' draft limitation.  The winglets on the AC boats fit the boats to the rule, deeper keels would have been superior (for performance) in all respects.  The winglets on airliners, initially, fit them into their parking spaces.

The 787, freed by larger spaces, exploits the advantage of not having winglets.  Its outer span has subtle shaping and shape changing flexibility which add to that advantage in a way that tacking on even clever winglets to unconstrained span do not - the A380 has little winglets both for marketing and to simplify adding virtual span long after the initial design.  Winglets are being marketed as well to all sorts of smaller General Aviation aircraft - both for span constraints in existing hangars, and for marketing, and, again, and ultralight tack-on is simpler in every way than redesign and renovation of an existing wing.

Difficulty & Subtlety of Increasing Effective Span.  Draft constraints on keels can be sharp, or just desirable, so the search for lower CG and greater effective span is quite legitimate.  But very difficult to get right.  Scheel headed in the right direction, but understandably, missed.  If someone other than Burt Rutan designs a Canard airplane, watch out.  If a team tacks winglets on a 12 metre without the insight and analysis of the early Australian boat, hold that bet.  The twin keels are a great alternative either side of the English Channel for sitting down gracefully when the tides out without resorting to stilts, but they are not a match for performance for the same effective deeper single span (and sitting down can be a lot worse than graceful.)

If Scheel had gone further: a gentler, truly progressive increase in foil thickness toward the base of the keel, and a near-sharp edge at the base as virtual fence (with zero surface area) for flow (pressure) escaping below, before reaching the trailing edge.  Perhaps progressing to a foil at the base which is net more effective at higher foil thickness.  It might have worked quite well.  Searching for lower VCG, "Marry it or Divorce it": a keel should lift, a bulb should be as invisible as possible (not easy), not lifting or dragging more than inevitable.

Inherent Disadvantage.  Winglets will only get you a virtual span increase of 1/2 or a little more of their own span.  And they'll generally have twice the surface area (or more), of simple span increase.  They'll introduce interference drags the simple span lacks. 

Advances in other keel shaping to reduce induced drag (the "bad" wake vortices) might change those deficits.  You won't have to wait for an example: Centerboards.

At first sight, a long post wouldn't seem to simplify anything, but sometimes seeing that a situation is simpler than it appears gets complicated.  

regards,

The wings add no righting moment , only lateral resistance 

hence these un ballasted  wings cause the boat to “trip “

hard to justify wings 

a well drawn scheel  keel works well 

 

[Santanasailor]

First, we sail a wing keel boat because that was what was available when we dirt poor horse trainers wanted to get back on the water.  We found one that was in really excellent condition at a price we could afford. We have owned several before and since, but the Wing Keel Santana 20, Anna Eleise is the one that stays in our family.  We sail this boat not because it has a wing keel, but because we found a boat we liked and purchased her Despite the wing keel.  In the end, we do appreciate the advantages this keel offers.  

Second being a student of aviation and a licensed pilot I concur with what GRR said. Winglets increase a wings efficiency by reducing the vortices coming off of the wing tips.  

The design of the wing on the Santana’s keel could offer some lateral resistance when the angle of heel is fairly steep (not the best condition to sail a Santana or any small IOR influenced design.  They like being sailed flat) Also, the quantity of lead in those wings offers a fair amount of righting ability.  All of which was never the idea of having winglets on the end of a wing.  

It is rumored that the Santana wing keel is faster than the full keel under very light wind conditions.  This is rumor, i have seen no data and I suspect the sails and or the sailor would make a greater difference under normal light air conditions.

I see a need for “winglets” on shoal draft keels.  The full wings that seemed to be in such a vogue a few decades ago, are to me really just a marketing fad that seemed to work to a certain degree, just as a bulb would work.    However, anything you have to drag though water is going to be…a drag.  

 

[Steam Flyer]

It's fairly common for shoal draft versions of boats to have more ballast than their deep keeled sisters to make up the loss in righting moment.    As an example, my boat has about 10% more ballast than the deep keel version.   And the shoal draft keel often has more wetted surface and drag than the deep keel.   So the shoal draft version can be slower on all points of sail.

My impression is that the wing keel fad has died down somewhat and most current production shallow draft keels just use a bulb like or flaired shape to get the ballast low enough for the required righting moment. 

Of course a shoal draft boat is far faster than a deep keel boat if the water is shallow enough.

What, sticking the keel into the bottom does not form an effective end plate??

I think this is really the issue. It's not strictly the efficiency of the keel at it's two tasks, it's how much it enables you to go places that deeper keel would rule out and how much you give up for that. It takes a really well-designed and well-executed wing keel to be better than just sawing off the keel at depth X and adding a streamlined bulb. Most are not all that well-designed.

One benefit of wings that I haven't seen mentioned... they damped motion. They dampen the vertical motion or 'heave' which is one of the components that induce sea sickness the most. And if the keel is forward or aft enough of the center of pitch rotation, they can dampen pitching nicely too. I did some sailing on a mid-1990s Bavaria with a rather forward-set wing keel that was notable for it's smooth motion in a chop.

- DSK

 

[The Q]

One problem for those of us who sail with a muddy bottom. Is a winged keel gives more chance of getting really stuck in the mud.

I spent hours considering winged keel designs for my little boat, but came to the conclusion.

A, I didn't have access to suitable computing programmes or testing facilities to design one.

B, As you tack off a river bank, a wing would require keeping off the bank further.

C, The boat would need an even shorter keel to avoid ploughing the bottom with the wings while heeled.

So in the end I went for a airfoil shaped thickened by 30% bottom 1/5 of the keel in which all the lead lives..

 

[Ease the sheet.]

What, sticking the keel into the bottom does not form an effective end plate??

I think this is really the issue. It's not strictly the efficiency of the keel at it's two tasks, it's how much it enables you to go places that deeper keel would rule out and how much you give up for that. It takes a really well-designed and well-executed wing keel to be better than just sawing off the keel at depth X and adding a streamlined bulb. Most are not all that well-designed.

One benefit of wings that I haven't seen mentioned... they damped motion. They dampen the vertical motion or 'heave' which is one of the components that induce sea sickness the most. And if the keel is forward or aft enough of the center of pitch rotation, they can dampen pitching nicely too. I did some sailing on a mid-1990s Bavaria with a rather forward-set wing keel that was notable for it's smooth motion in a chop.

- DSK

Damping hey?

Doesn't the whole boat move with the wave equally? In deep water at least....

And by "the whole boat" I mean the more technical* term, not bows or transoms.....

*Center of gravity?

 

[The Q]

The simple answer the that is the vertical movement up and down of the boat is pulling or pushing water over the wings if they are big enough to notice the effect. The water in a wave does not move equally from surface to the bottom of the keel. The boats vertical movement drags a large amount of water with it.

Big area keel wings like this one are known to have a large damping effect.

 

[Zonker]

I think that >90% of winged keels are very ugly from a hydrodynamic point of view. Most of the wings are just a place for extra ballast and lots of extra wetted surface area. I think a well designed bulb is a smarter way to maximize volume/minimal drag.

#1 All the surface area we can create

#2 very bad bulb shape. wing profile looks suspect too.

#3 way too much squish in the bulb. Little squish good to lower VCG but too much is just too much wetted surface area

#4 basic keel planform shape looks wrong. fin profile looks wrong.

#5 probably does least harm

#5,6  fins too short for any tip vortex reduction effect

          

       

 

[The Q]

Yep most wings shown were a fashion statement.. marketing said put a wing on, without a budget for proving the shape..

And the other reason for not having them.. weed and lobster pots. That's why I would never have a forward projection below the waterline , nor wings like that once I'd thought about it. The closest I'd have would be a beaver tail .

 

[Steam Flyer]

Yep most wings shown were a fashion statement.. marketing said put a wing on, without a budget for proving the shape..

And the other reason for not having them.. weed and lobster pots. That's why I would never have a forward projection below the waterline , nor wings like that once I'd thought about it. The closest I'd have would be a beaver tail .

It's like having the bottom of your keel molded to the shape of a Bruce Anchor... who wouldn't want that?!?

Damping hey?

Doesn't the whole boat move with the wave equally? In deep water at least....

And by "the whole boat" I mean the more technical* term, not bows or transoms.....

*Center of gravity?

Yes, the whole whole boat moves with the wave but unless the water is also moving up and down equally, horizontal surface will do something good for once, and dampen the motion thru the water. As Zonker says, it's almost certainly not worth the added drag of that surface area in the first place.

- DSK

 

[Ease the sheet.]

It's like having the bottom of your keel molded to the shape of a Bruce Anchor... who wouldn't want that?!?

Yes, the whole whole boat moves with the wave but unless the water is also moving up and down equally, horizontal surface will do something good for once, and dampen the motion thru the water. As Zonker says, it's almost certainly not worth the added drag of that surface area in the first place.

- DSK

It's a wave, it moves up and down. Equally...

In practice, there may indeed be a dampening effect. In theory, I'm not so sure.

 

[Steam Flyer]

It's a wave, it moves up and down. Equally...

In practice, there may indeed be a dampening effect. In theory, I'm not so sure.

Wave mechanics isn't really my area of expertise, but the water underneath and within a wave does not move as much as the surface. If it did, it wouldn't look like a wave. It would be the whole ocean moving up and down. Probably shake the planet.

- DSK